A number of power supply arrangements are presently commercially available to provide a precise output irrespective of the variations in AC input voltage and changes in the load. As disclosed in U.S. Pat. No. 3,414,798 issued to Jorgen L. Nielsen on Dec. 3, 1968, one type of power supply is a switching device for selectively turning on and off the input voltage. In this power supply the input voltage is provided to rectifying and filtering networks which develop the desired output voltages. A feedback control loop samples the output of the power supply and provides the sampled voltage output to a comparison circuit which compares the sampled output with a reference voltage. A control signal is developed by the comparison circuit which is used to operate the switching device to switch on and off the input voltage at a rate to make the output voltage constant.
The prior art power supplies, however, have disadvantages in that generally it is more difficult to sample voltage output as voltage and make comparison thereof than to sample voltage outputs as current and make comparison thereof. Further such prior art devices provide no compensating signal to the reference source to compensate for the error signal. Also there is generally no consideration given to synchronizing the timing of switching on the input voltage at the same point in the cycle thereof in order to provide a precise voltage output.